The present invention relats in general to graft terpolymers and stable aqueous emulsions thereof and, in particular, to stable, aqueous dispersions or latices containing dispersed particles comprising a polymeric N-vinyl lactam having grafted thereon as side chains, units of an alkyl ester of an .alpha.-.beta.-unsaturated carboxylic acid and a monoacid ester of an unsaturated dibasic acid.
Graft copolymers comprising a basic homopolymer chain having grafted thereon units or a plurality of such units of one or more polymerizable monomers, in chain form represent an interesting and important development in the resin arts, particularly since such graft copolymers find immediate and practical utility for the resin chemist to utilize them as "building block" resin systems or "module" resin systems which can be employed to "tailor-make" subsequent resin systems to quite specific industrial needs. Grafted copolymers can be made by a variety of polymerization methods including solution, emulsion or bulk polymerization and the like.
Copolymers of N-vinyl lactams, and particularly N-vinyl pyrrolidone, with various unsaturated compounds, are well known in the art and have een used in industry as coatings, textile sizes, adhesives and the like. However, in the formation of these polymers previously, it has not been possible to introduce carboxylic acid groups into the copolymers without decomposition of the N-vinyl lactam caused by a devinylation side reaction. U.S. Pat. No. 3,686,150 has, however, formed straight interpolymers thereof. Polymers containing carboxylic acid groups are highly desirable, as such groups represent a functionality useful for yielding a wide variety of products.
In another recently issued patent of the same assignee, U.S. Pat. No. 3,511,817, there is disclosed and claimed film-forming copolymers of N-vinyl lactams, e.g. N-vinyl pyrrolidone, and mono or half esters of unsaturated dicarboxylic acids, the copolymers being produced by the copolymerization of a preformed half ester of an unsaturated dicarboxylic acid, with an N-vinyl lactam in the presence of a polymerization catalyst. This is, however, only an interpolymer, and its preparation can be made only in organic reaction media, which are solvents of the interpolymer.
The present invention provides a graft emulsion terpolymer of the monomers of U.S. Pat. No. 3,686,150, the properties of which can be varied over a very wide range while still retaining the valuable carboxylic acid function.
Graft copolymers, as is well known in the art, may be prepared by the irradiation of free radical polymerization of solutions of linear homopolymers in another monomer or monomers. The reaction mechanism is believed to cause the dislodgement of hydrogen atoms or ions, forming activated centers along the homopolymer chain from which branches grow, the latter produced copolymer being in contrast to an interpolymer. Inasmuch as the graft copolymer has a much "coarser" alternation of units than does the interpolymr, the chemical properties thereof are affected. Graft copolymers tend to exhibit properties of each of the monomeric units, in contrast to interpolymers which only exhibit properties intermediate between those of the monomers.